The present invention relates to a purely mechanical lock device of the pushbutton system dispensing with a key and more particularly to a lock device of the type described which is of a mortise lock type.
As a prior-art lock device of a purely mechanical pushbutton type which dispenses a key, a padlock comprising two lock units is known in Japanese Laid-open patent application No. 55499/1975, which is constructed in such a manner that pushbuttons of a number r out of a total number of n are mechanically operated to the requirements for redering the padlock inoperative which conform to the permutation.
Further, a lock device of a mortise lock type using the lock units of the above-mentioned padlock is also proposed in Japanese Laid-open patent application No. 69799/1978. This lock device comprises a latch bolt operating mechanism capable of projecting a latch bolt into a mortise of a door and withdrawing the same from the mortise by turning a grip for opening and closing the door; a dead bolt operating mechanism for withdrawing the dead bolt into an end edge of the door through the latch bolt operating mechanism only when the lock units are in the unlocked state; an indoor unlocking mechanism for operating freely the dead bolt from inside the room; and a resetting mechanism for returning the lock units to the standby position by turning the grip for one receprocating operation of a reset lever.
In the lock device, the grip portion is disposed beside the above-mentioned mechanisms, and a locking and unlocking pawl of a locking and unlocking member connected to a locking and unlocking bar is made of an upright plate member. This requires that the locking and unlocking pawl be made comparatively great in height in order to move the dead bolt between a locked position in which the dead bolt is projected into the mortise and an unlocked position in which the dead bolt is withdrawn from the mortise. Therefore, in comparison with the conventional lock devices requiring keys, the lock device disclosed in Japanese Laid-open patent application No. 69799/1978 is wider and thicker, so that some difficulties are encountered when the lock device is attached to ordinary doors. Stated differently, the ordinary door comprises an outer frame, and a lock device is usually fitted within the frame. However, since the above-mentioned lock device is comparatively wide and thick, part of the frame of the door has to be cut off for attaching the lock device to the door, which may weaken the door and may cost much. Furthermore, the grip has to be located away from the usual position in the direction of the center of the door.
In the conventional lock device, when the dead bolt is in the locked position, the dead bolt itself is not locked at all, but it is simply projected into the mortise. Therefore, the dead bolt cannot be maintained fixedly in the locked position. Therefore, there is a risk that the dead bolt can be withdrawn from the mortise with ease when the door is vibrated or the dead bolt is moved by use of a pin or the like. This is a shortcoming of the conventional lock device in view of the safety.
Further, in the conventional lock device, a control slider includes a seesaw member, and a control pin of the seesaw member is brought into engagement with a notch of an intermediate slider, whereby the control slider is connected to the intermediate slider. However, a control projection for controlling the seesaw member of the control slider is secured to the dead bolt, so that the dead bolt is completely in the free state except at a position in which the dead bolt is completely moved to the unlocked position. In other words, the intermediate slider and the control slider are connected to each other in the locked state. However, since the dead bolt is completely in the free state, if the dead bolt is moved between the unlocked position and the locked position for some reason, the control projection is also moved together with the dead bolt. Therefore, the control pin disengages from the notch of the intermediate slider. In this case, even if the lock units are in the unlocked state, the dead bolt cannot be moved by turning the grip. This is a problem to the dead bolt operating mechanism.
Furthermore, the lock unit employed in the abovementioned conventional lock device comprises a rotatable locking and unlocking bar which is in engagement with a locking and unlocking member; a permutation driving plate and a permutation driven plate which are indenpendently moved by a predetermined distance (hereinafter referred to as one stage) when their respective pushbuttons are depressed, and a sliding plate which is carried by the permutation driven plate and is capable of moving relative to the permutation driven plate in a direction parallel to the permutation driven plate. In the lock unit, the sliding plate is carried by the permutation driving plate and is then further moved by the permutation driven plate from a rotation prevention position in which the locking and unlocking bar cannot be rotated to a rotation prevention release position in which the locking and unlocking bar can be rotated.
Further, in Japanese Laid-open patent application No. 55499/1975 there is desclosed a lock unit provided a safety plate which is operated by depressing a pushbutton which belongs to the safety plate and is different from the pushbuttons belonging to the permutation driving plate, the permutation driven plate and the sliding plates. The safety plate is capable of moving relative to the locking and unlocking bar, that is, from the rotation prevention position to the rotation prevention release position and vice versa.
A lock unit of the permutation operation type described can make a great contribution to making lock devices small in size by combining the safety plate and the movable permutation plates appropriately, and to the guarantee of safety by disposing pushbuttons which must not be depressed for unlocking the lock devices.
However, the lock unit mentioned above has a shortcoming in that there are several modes of depressing the pushbuttons of the lock unit for bringing the lock unit to the unlocking state (hereinafter referred to as unlocking-pushbutton-depression mode).
Let us assume that there are four pushbuttons W, X, Y and Z, which respectively belong to a permutation driving plate, a permutation driven plate, a prevention operation safety plate and a relase operation safety plate. In this lock unit, the unlocking requirement is met when the pushbutton W is depressed prior to the depression of pushbutton X, and the pushbutton Y can be depressed any time. Therefore, there are three unlocking-pushbutton-depression modes, WXY, WYX and YWX. On the other hand, in another lock unit, if the pushbutton W is for a permutation driving plate; the pushbutton Y for a permutation driven plate; the pushbutton X for a prevention operation safety plate and the pushbutton Z for a release operation safety plate, the unlocking-pushbutton-depression modes are WYX, WXY and XWY. Comparing these pushbutton depression modes with the above-mentioned unlocking-pushbutton-depression modes, WXY and WYX modes are common. Therefore, the two unlocking-pushbutton-depression modes WXY and WYX satisfy the unlocking requirement of both lock units.
Furthermore, the unlocking requirement of the above-mentioned lock units with respect to the permutation driving plate and the permutation driven plate is that the sliding plate be moved by one stage in accordance with the movement of the permutation driving plate, and the sliding plate be then moved by another stage together with the permutation driven plate, so that the sliding plate be moved by two stages. Therefore, if the permutation driven plate is moved before the permutation driving plate is moved, the sliding plate is not pushed by the permutation driving plate. The result is that the sliding plate is moved only one stage and, the unlocking requirement is not met in this case.
In the conventional lock units, if the permutation driven plate is moved before the permutation driving plate, the sliding plate is advanced, due to the inertia force thereof, relative to the permutation driven plate when the permutation driven plate is stopped. If the advanced distance of the sliding plate from the permutation driven plate nearly equals one stage, it causes a malfunction in the lock units, so that the lock device is unlocked when it must not be unlocked.
Furthermore, in the conventional lock units, the sliding plate is held tightly by a plate spring situated above the sliding plate when the sliding plate is stopped and the space for the plate spring makes it difficult to make the lock units thinner.